1. Field of the Invention
The present invention relates to a method of making a second pole tip of a write head with a narrow track width and more particularly to a method of trimming an oversized second pole tip to a desired track width while maintaining a desired height thereof.
2. Description of the Related Art
A write head is typically combined with a magnetoresistive (MR) read head to form a merged MR head. The merged MR head has thin film layers that have edges exposed at an air bearing surface (ABS) for writing and receiving magnetic fields on a magnetic medium, such as a disk or tape drive. The write head comprises first and second pole pieces connected at a back gap which is recessed from the ABS. The first and second pole pieces have first and second pole tips, respectively, which terminate at the ABS. An insulation stack, which comprises a plurality of insulation layers, is sandwiched between the first and second pole pieces and a coil layer is embedded in the insulation stack. A processing circuit is connected to the coil layer for providing a write current that is conducted through the coil layer which, in turn, induces write fields in the first and second pole pieces. A non-magnetic gap layer is sandwiched between the first and second pole tips so that flux fringes across the gap layer at the ABS. In a magnetic disk drive, a magnetic disk is rotated adjacent to and a short distance from the ABS so that the flux magnetizes the disk along circular tracks. The written circular tracks then contain magnetized segments with fields detectable by a read head.
An MR read head includes an MR sensor sandwiched between first and second non-magnetic gap layers and having an edge located at the ABS. The first and second gap layers and the MR sensor are sandwiched between first and second shield layers. In a merged MR head the second shield layer and the first pole piece are a common layer. The MR sensor detects magnetic fields from the circular tracks of the rotating disk by a change in resistance which corresponds to the strength of the fields. A sense current conducted through the MR sensor results in voltage changes that are detected by the processing circuitry as readback signals.
One or more merged MR heads may be employed in a magnetic disk drive for reading and writing information on circular tracks of a rotating disk. A merged MR head is mounted on a slider carried on a suspension. The suspension is mounted to an actuator which rotates the magnetic head to locations corresponding to desired tracks. As the disk rotates an air cushion is generated between the rotating disk and an air bearing surface (ABS) of the slider. A force of the air cushion against the air bearing surface is opposed by an opposite loading force of the suspension, causing the magnetic head to be suspended a slight distance (flying height) from the surface of the disk. Flying heights are typically on the order of about .05 .mu.m.
Areal or bit density of a write head indicates the number of bits that can be written to a square inch of magnetic media, such as a magnetic tape or magnetic disk. Areal density is a product of linear density and track density of the write head. Linear density is the number of field transitions that can be written per linear inch along a track, while track density is the number of tracks that can be written per inch of track width. Linear density depends upon the distance between the first and second pole tips of the write head at the ABS. This distance (the "gap length") is equal to the thickness of the write gap layer at the ABS. "Track width" is a measure of the width of the second pole tip of the write head at the ABS. The narrower the second pole tip, the less the track width, and the greater the track density. Both the thickness of the write gap and the narrowness of the second pole tip have received intensive research to improve areal density. The focus of the present invention is to reduce the width of the second pole tip and increase track density, without sacrificing definition of the second pole tip itself.
The second pole tip is typically constructed by frame plating. After forming the first pole piece layer, a write gap layer, and a plurality of insulation layers with a coil layer embedded therein, a photoresist layer is spun on the write gap layer and a top insulation layer. The insulation layers comprise an insulation stack. Unfortunately, the insulation stack contributes to the height of the partially completed write head in a yoke region which is immediately behind a pole tip region. This increases the thickness of the photoresist layer in the pole tip region where the second pole tip is to be formed. Light is directed into the photoresist layer to expose portions that are to be removed by developing for forming the second pole piece in the yoke and pole tip regions. The light scatters to an increasing degree with increasing depth of the photoresist layer. Because of the greater depth of the photoresist layer in the pole tip region, light scattering toward the bottom of the resist can pose a problem when the exposed photoresist is developed for removal. After removal, the photoresist in the pole tip region has side walls that slope inwardly instead of being vertical. This inward slope of the side walls diminishes the definition of the second pole tip. A more serious problem is that the insulation stack has a front sloping light reflecting surface that faces the pole tip region. Light is irregularly reflected from this surface into the pole tip region. Upon developing the photoresist, the side walls of the photoresist in the pole tip region are irregular instead of being planar. The result is a poorly shaped photoresist frame in the pole tip region for forming the second pole tip. The next steps are to plate the second pole piece layer in the opening of the photoresist frame and remove the frame in a dissolvent. The poor shape of the photoresist frames causes the side walls of the second pole tip to be irregular and slanted.
In order to overcome the aforementioned problems of frame plating the second pole tip, the thickness of the photoresist in the pole tip region is kept to an acceptable level. This level is determined by the ratio of the thickness of the photoresist in the pole tip region to the track width of the second pole tip, which is known in the art as the "aspect ratio". An acceptable value for the aspect ratio is four, which implies that the thickness of the photoresist in the pole tip region should be no more than four times the track width of the second pole tip. It can be seen that this can be a serious limitation in constructing a narrow second pole tip. To construct a second pole tip with a 1 .mu.m track width, the photoresist can be no more than 4 .mu.m high in the pole tip region. This is very difficult to achieve in view of the height of the insulation stack. Thus, there is a strong-felt need to construct a well-defined second pole tip with a submicron track width.